The present invention relates to a flat plate antenna, and particularly but not solely to an antenna for the reception of Direct Broadcast Satellite (DBS) television signals.
It is proposed that DBS networks will operate on a carrier frequency of around 12 GHz. Flat plate antennas for this frequency range are made of an array of elements, each element being capable of receiving the 12 GHz signals. Due to the short (2.5 cm) wavelength involved the elements are small in size. To provide sufficient energy for satisfactory television pictures, a large array of elements is needed. For aesthetic reasons this array should not be larger than about one square meter. The received signal from each of these elements has to be guided, in the correct phase relationship, to a common point so that the combined signal can be fed into the front end module of the receiver. However, in the transfer of these individual signals to the common collecting point, a substantial proportion of the signal can be lost.
One form of flat plate antenna, described in European Patent Application Publication No. 132945, has four arrays each having sixteen helical antenna elements with probes located within a common resonant cavity of square cross-section. The cavity is used to combine all the outputs of the elements with very low loss.